1. Field of the Invention
The present invention relates to a control device and method for an internal combustion engine, and in particular relates to a control device and method for controlling an internal combustion engine which is equipped with a variable valve operation device capable of varying the opening characteristics of the valves.
2. Description of the Related Art
In Japanese Patent Laid-Open Publication 2004-143990, there is disclosed a control device for an internal combustion engine, equipped with a valve operating mechanism which is built so as to make it possible to suspend the valve opening operation of the intake valves and the exhaust valves. With this control device, in order to prevent deterioration of the catalyst due to flow-through of air when the fuel is cut off, it is arranged to suspend the valve opening operation (i.e. to keep in a closed state) of at least one of the intake valve and the exhaust valve of a plurality of cylinders.
Furthermore, with this control device, it may be arranged to suspend the valve opening operation of one only of the intake valve and the exhaust valve of a plurality of cylinders; and thereby the beneficial effect of engine braking is obtained by creating pumping loss. According to this type of control, although sometimes, when the fuel is cut off, the operation of one of the intake valves and the exhaust valves is suspended with a view to preventing deterioration of the catalyst, nevertheless it is still possible to keep the beneficial effect of engine braking, so that it is possible to obtain a feeling of deceleration.
The operational timings of the pistons in the engine cylinders are relatively different from one another, and depend upon factors such as the number of cylinders, the type of the engine (whether it is an in-line type engine or a V-type engine), the firing intervals between the various cylinders, and so on. Accordingly in order effectively, during fuel cut-off, to prevent flow-through of air to the catalyst while still ensuring engine braking, it is desirable to select, from among the plurality of cylinders, those cylinders for which the valve opening operation of the valves must be suspended, in consideration of the fact that the operational timings of the pistons are different for the different cylinders. No attention is paid to this matter with the above described control device, and accordingly there still remains unexplored scope for research with regard to implementation of a system for, during fuel cut-off, effectively preventing flow-through of air to the catalyst, while also ensuring good engine braking.